1. Technical Field
The present invention relates to an image forming apparatus and image forming method capable of double-sided printing.
2. Related Arts
There is an image forming apparatus that has a circulating transfer route including a sheet reversal path. This apparatus performs, when a one-sided printing is selected, the one-sided printing by printing on one side of a print medium and then discharging the printed print medium without using the sheet reversal path and at the same time, and performs, when a double-sided printing is selected, the double-sided printing by printing on one side of a print medium and at the same time, printing on the other side by transferring the print medium on the one side of which printing is performed through the circulating transfer route to reverse the print medium.
In such an image forming apparatus capable of a double-sided printing, when the double-sided printing is performed on print media of two or more kinds of sheet sizes, the transfer speed at which the sheet is transferred through the circulating transfer route differs depending on the sheet size, and therefore, it is necessary to perform printing for each sheet size. Because of this, the waiting time for transfer of the print medium is long and a considerable time is required to complete printing.
Japanese Patent No. 3880281 proposes an image forming apparatus comprising a first detector detecting a state of waiting for a print medium being transferred along a circulating path to be fed again, a second detector detecting a state of waiting for a sheet for double-sided image formation and a sheet for one-sided image formation to be fed by a feeding unit, a determining unit determining whether or not there is a sheet for double-sided image formation in a range from the foremost sheet waiting to be fed to the last sheet waiting to be fed of the sheets, the number of which is twice the number of sheets for double-sided image formation waiting to be fed again, based on the detection results of the first detector and the second detector, and a control unit controlling so as to feed, when there is a sheet for double-sided image formation in the range of the sheets waiting to be fed, the foremost sheet waiting to be fed by regarding it as a sheet for double-sided image formation and to feed a sheet again along the circulating path.